If mammalian cells receive a go-ahead signal at the `G_(1)` checkpoint, they will

Options

A. move directly into telophase.
B. complete the cycle and divide.
C. exit the cycle and switch to a nondividing state.
D. show a drop in MPF concentration.

Answer

To answer the question about what happens if mammalian cells receive a go-ahead signal at the G1 checkpoint, we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding the G1 Checkpoint**:
- The G1 checkpoint is a critical control point in the cell cycle that occurs towards the end of the G1 phase. It assesses whether the cell is ready to proceed to the next phase (S phase) of the cell cycle.

2. **Receiving the Go-Ahead Signal**:
- If the cell receives a go-ahead signal at this checkpoint, it indicates that the cell has met all the necessary conditions to continue. This includes checking for DNA damage, sufficient nutrients, and appropriate growth signals.

3. **Transition to S Phase**:
- Upon receiving the go-ahead signal, the cell will transition from the G1 phase into the S phase. During the S phase, the cell replicates its DNA in preparation for cell division.

4. **Completion of the Cell Cycle**:
- After successfully completing the S phase, the cell will continue through the subsequent phases of the cell cycle, which include G2 phase and mitosis (M phase), ultimately leading to cell division.

5. **Final Outcome**:
- Therefore, if a mammalian cell receives a go-ahead signal at the G1 checkpoint, it will complete the cell cycle and divide.

### Final Answer:
**B. Complete the cell cycle and divide.**

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